This research program proposes to examine biochemical relationships between steroid hormones and expression of reproductive behaviors in mammals and birds. Readily quantifiable behaviors (e.g. lordosis reflex and male sexual behavior in mammals, and courtship and incubation behaviors in birds) are selected for this study of hormone-behavior interactions. There are four interlocking aspects to the program. First, by means of recent radioimmunoassay methods, endogenous gonadal steroids will be measured in relation to display of reproductive behaviors. Once the nature and pattern of normally secreted hormones have thus been determined, the second phase is reached. This consists of attempts to localize brain areas in which steroids act to facilitate or inhibit display of reproductive behavior. These localization techniques include implantation of steroids into brain, systemic administration of radioactive steroids to determine loci at which hormones are selectively metabolized or retained, and subcellular fractionation of brain areas exposed to radioactive steroids. The next phase of the research deals with biochemical effects of steroids on brain protein synthesis in relation to behavior. Some animals are more sensitive than others to the effects of steroids. The question of what factors influence behavioral sensitivity to steroids forms a fourth phase of this program. Factors involved in differential steroid sensitivity (e.g. species, developmental age, and level of sexual activity) will be examined for possible correlations with secretion, uptake and metabolism of steroids.